In the related art, the time-sharing process (Time Sharing System) has been adopted for processing plural analog signals.
To simply describe this signal processing system, this is a system for sequentially processing signals when one signal processing circuit such as, for example, only one amplifier circuit or AD (i.e., Analog to Digital) converter is provided. During a certain time period, a first analog signal is processed; during a subsequent time period, a second analog signal is processed; and during a further subsequent time period, a third analog signal is processed.
Such processing is an extremely clear system, but, on the other hand, a principal problem is present. For example, during a time period in which the first analog signal is processed, no other analog signal can be processed. Accordingly, the greater the number of analog signals, the greater will be the number of signals that are discarded without being processed. As a result, a phenomenon with deterioration of an SN ratio (i.e., Signal to Noise Ratio) of the signal occurs.
As a measure for overcoming such a problem, there has been known what is described in, for example, Patent Document 1. This measure is implemented mainly for sensor signals such as analog signals, and has a feature that plural signals are linearly combined in different combinations.
Generally speaking, such a measure is a type of modulation mentioned above and there exist only three types of modulating measures including “non-inverted signal” (i.e., the original sensor signal remains unchanged), “non-signal”, and “inverted signal”. Further, these three types can be constructed of only switches, thereby making it possible to expect a remarkable cost reduction and a reduction of power consumption while simultaneously improving the SN ratio.